MRL mice homozygous for the lpr (lymphoproliferation) gene (MRL-lpr/lpr) develop lymphadenopathy, splenomegally and autoimmune disease characterized by hypergammaglobulinemia, autoantibody production, arthritis and glomerulonephritis. The lpr gene has not been mapped and is defined only by the autoimmune phenotype. Adult MRL-lpr/lpr mice develop a 100 fold increase in T cells in lymphoid organs. The majority of these T cells are an immature CD4-8- phenotype and express a normal T-cell receptor alpha- beta heterodimer. These mice have been extensively studied as a mouse model of human autoimmune disease and is the only autoimmune mouse model that spontaneously develops arthritis. However, the molecular and cellular basis underlying the lymphoproliferative autoimmune syndrome is unknown. Extensive studies of these mice suggest that T cells undergo abnormal maturation during thymic development prior to induction of self tolerance. These results have led to the suggestion that excessive production of immature autoreactive T cells migrate from the thymus in large numbers to populate the spleen and lymph nodes. The autoreactive T cells have been proposed to be stimulated by self antigens in the periphery, expand, and produce factors that drive B cells to proliferate, differentiate, and produce immunoglobulins and autoantibodies. The present proposal will study MRL-lpr/lpr and C57BL/6-lpr/lpr mice that expresses a transgenic self-reactive T-cell receptor alpha and beta chain on 95% of thymic and peripheral T cells to directly determine if self-reactive T cells exit the thymus in large numbers and are self reactive in the peripheral lymphoid organs. Autoimmune lpr/lpr mice that have been backcrossed to a transgenic mouse that expresses the T-cell receptor for the H-2Db restricted male H-Y antigen will be used for these experiments. The T-cell receptor beta chain uses the Vbeta8.2 region, detected by the anti-Vbeta8 antibody F23.1. This allows easy identification of the transgenic T-cell receptor by flow cytometry or immunohistochemistry. Transgenic autoimmune lpr/lpr mice and control mice will be analyzed to determine the effect of the lpr gene on positive selection on H-2b thymic stroma (by comparison of lpr/lpr and +/+ H-2b female mice) and negative selection on H-2b+H-Y+ thymic dendritic cells (by comparison of lpr/lpr and +/+ H-2b male mice). A possible defect in induction of clonal anergy in the thymus and periphery will be studied by first crosslinking the TCR or CD3 molecules followed by analyses of proliferation, IL-2 expression, phosphorylation and gene expression. In order to identify the stages of abnormal thymocyte or peripheral T cell development, TCR transgenic lpr/lpr and control mice will be analyzed after pulse labeling of CD4-CD8- thymocytes with BrdU or after irradiation and bone marrow transfer. Experiments outlined in this proposal should allow the identification of abnormalities of intrathymic and extrathymic differentiation of autoreactive T cells in lpr/lpr mice and elucidate cellular and molecular mechanisms behind abnormal clonal deletion and anergy induction of self-reactive T cells.